Exemplary embodiments relate to a semiconductor memory device and a method of operating the same and, more particularly, to a page buffer including a dynamic latch and a sense operation using the page buffer.
A semiconductor memory device includes page buffers for storing external program data when a program operation is performed and a memory cell array for storing data depending on the program data stored in the page buffers.
Furthermore, the page buffer performs a sense operation for a program verification operation in a program operation and, in a read operation, performs an operation of sensing the voltage level of a bit line, shifting depending on whether a selected memory cell has been programmed, and storing the voltage level in the form of data.
The page buffer may perform the sense operation by controlling the level of voltage supplied to the gate of an NMOS transistor or a PMOS transistor. However, the method of controlling the level of voltage supplied to the gate of the transistor may reach limits as to a fine sense operation.
For example, the sense operation of the page buffer using only a static latch is described as follows. When a read voltage is supplied to a word line coupled to a selected memory cell, the voltage level of a precharged bit line shifts or remains intact depending on the level of a threshold voltage of the selected memory cell. When the voltage level of the bit line is determined as described above, the page buffer senses the voltage level of the bit line and outputs data of the latch which changes or remains intact depending on the sensed voltage level. Next, a control circuit determines whether the data outputted from the page buffer is ‘1’ or ‘0’.
The sense operation of the page buffer using the dynamic latch is described as follows. The page buffer using the dynamic latch determines the voltage level of the bit line depending on data of the selected memory cell. The page buffer stores the determined voltage level of the bit line in a sense latch, compares the data stored in the sense latch and the data stored in the dynamic latch, and outputs data corresponding to a result of the comparison. Next, the control circuit determines whether the data outputted from the page buffer is ‘1’ or ‘0’.
As described above, a conventional page buffer performs the sense operation by sending the amount of current flowing depending on a voltage supplied to the gate of the transistor. However, such a sense method may reach limits in measuring a shift in fine current level of nano ampere (nA).